This invention relates, in general, to acceleration sensing devices, and more specifically, to micromachined acceleration sensing devices which determine the distance travelled by an object.
Acceleration sensing devices such as accelerometers are used in a variety of commercial and military applications. The automobile industry, for example, uses accelerometers to activate certain safety devices, such as air bags, during accidents. In military applications, accelerometers aid in measuring the velocity or distance travelled by a missile or projectile during flight. This allows the missile's or projectile's fuze to be armed at the appropriate distance along the missile's or projectile's trajectory. Such accelerometers require sophisticated electronic circuitry to provide a measure of time. The time and the output from the accelerometer are combined in a microcomputer which integrates the output over time to yield velocity or distance travelled.
In the military arena, acceleration driven devices conventionally comprise a mechanical runaway escapement coupled to an eccentric gear. This type of accelerometer is double integrating, or in other words, measures a force caused by acceleration of the accelerometer and estimates the distance travelled by the projectile or missile to which it is attached. The major problem with the mechanical runaway escapement/eccentric gear accelerometers is the low accuracy and high probability of mechanical failure due to the high number of moving parts.